Elixir provides Path.wildcard, which uses the Erlang :filelib.wildcard function internally.
Matching is case-sensitive, for example, "a" does not match "A".
(http://erlang.org/doc/man/filelib.html#wildcard-1)
Please is there a case-insensitive alternative?
There's no built in option to do this, but since the wildcard syntax supports character alternations similar to regex, you can replace every letter with an alternation of its lower and upper case versions, e.g. f0o -> [fF]0[oO], and then pass that to Path.wildcard/1. Here's a simple implementation that does this for ASCII letters:
defmodule A do
def case_insensitive_glob(glob) do
Regex.replace(~r/[a-zA-Z]/, glob, fn letter ->
"[#{String.downcase(letter)}#{String.upcase(letter)}]"
end)
end
end
glob = A.case_insensitive_glob("**/*reAdmE.*") |> IO.inspect
Path.wildcard(glob) |> IO.inspect
Running this in the OTP source code produces all files with their name containing "reAdmE." in any case.
"**/*[rR][eE][aA][dD][mM][eE].*"
["README.md", "erts/emulator/pcre/README.pcre_update.md",
"lib/erl_interface/src/README.internal",
"lib/ic/examples/pre_post_condition/ReadMe.txt", "xcomp/README.md"]
I've verified the output's correctness with find:
$ find . -iname 'readme.*'
./erts/emulator/pcre/README.pcre_update.md
./lib/erl_interface/src/README.internal
./lib/ic/examples/pre_post_condition/ReadMe.txt
./README.md
./xcomp/README.md
Related
I'm trying to do a word search with regex and wonder how to type AND for multiple criteria.
For example, how to type the following:
(Start with a) AND (Contains p) AND (Ends with e), such as the word apple?
Input
apple
pineapple
avocado
Code
grep -E "regex expression here" input.txt
Desired output
apple
What should the regex expression be?
In general you can't implement and in a regexp (but you can implement then with .*) but you can in a multi-regexp condition using a tool that supports it.
To address the case of ands, you should have made your example starts with a and includes p and includes l and ends with e with input including alpine so it wasn't trivial to express in a regexp by just putting .*s in between characters but is trivial in a multi-regexp condition:
$ cat file
apple
pineapple
avocado
alpine
Using &&s will find both words regardless of the order of p and l as desired:
$ awk '/^a/ && /p/ && /l/ && /e$/' file
apple
alpine
but, as you can see, you can't just use .*s to implement and:
$ grep '^a.*p.*l.*e$' file
apple
If you had to use a single regexp then you'd have to do something like:
$ grep -E '^a.*(p.*l|l.*p).*e$' file
apple
alpine
two ways you can do it
all that "&&" is same as negating the totality of a bunch of OR's "||", so you can write the reverse of what you want.
at a single bit-level, AND is same as multiplication of the bits, which means, instead of doing all the && if u think it's overly verbose, you can directly "multiply" the patterns together :
awk '/^a/ * /p/ * /e$/'
so by multiplying them, you're doing the same as performing multiple logical ANDs all at once
(but only use the short hand if inputs aren't too gigantic, or when savings from early exit are known to be negligible.
don't think of them as merely regex patterns - it's easier for one to think of anything not inside an action block, what's typically referred to as pattern, as
any combination and collection of items that could be evaluated for a boolean outcome of TRUE or FALSE in the end
e.g. POSIX-compliant expressions that work in the space include
sprintf()
field assignments, etc
(even decrementing NR - if there's such a need)
but not
statements like next, print, printf(),
delete array etc, or any of the loop structures
surprisingly though, getline is directly doable
in the pattern space area (with some wrapper workaround)
I am writing an interpreter for assembly using lex and yacc. The problem is that I need to parse a word that will strictly be at the end of the file. I've read that there is an anchor $, which can help. However it doesn't work as I expected. I've wrote this in my lex file:
ABC$ {printf("QWERTY\n");}
The input file is:
ABC
without spaces or any other invisible symbols. So I expect the outputput to be QWERTY, however what I get is:
ABC
which I guess means that the program couldn't parse it. Then I thought, that $ might be a regular symbol in lex, so I changed the input file into this:
ABC$
So, if $ isn't a special symbol, then it will be parsed as a normal symbol, and the output will be QWERTY. This doesn't happen, the output is:
ABC$
The question is whether $ in lex is a normal symbol or special one.
In (f)lex, $ matches zero characters followed by a newline character.
That's different from many regex libraries where $ will match at the end of input. So if your file does not have a newline at the end, as your question indicates (assuming you consider newline to be an invisible character), it won't be matched.
As #sepp2k suggests in a comment, the pattern also won't be matched if the input file happens to use Windows line endings (which consist of the sequence \r\n), unless the generated flex file was compiled for Windows. So if you created the file on Windows and run the flex-generated scanner in a Unix environment, the \r will also cause the pattern to fail to match. In that case, you can use (f)lex's trailing context operator:
ABC/\r?\n { puts("Matched ABC at the end of a line"); }
See the flex documentation for patterns for a full description of the trailing context operator. (Search for "trailing context" on that page; it's roughly halfway down.) $ is exactly equivalent to /\n.
That still won't match ABC at the very end of the file. Matching strings at the very end of the file is a bit tricky, but it can be done with two patterns if it's ok to recognise the string other than at the end of the file, triggering a different action:
ABC/. { /* Do nothing. This ABC is not at the end of a line or the file */ }
ABC { puts("ABC recognised at the end of a line"); }
That works because the first pattern will match as long as there is some non-newline character following ABC. (. matches any character other than a newline. See the above link for details.) If you also need to work with Windows line endings, you'll need to modify the trailing context in the first pattern.
I just picked up Erlang and I ran into a simple problem, but I have not been able to fix it or find anything about it. I'm trying to define a module that checks if an atom is in a given list. I entered the list through the Erlang shell like this:
veggies:veggieMember([cucumber,tomato,potato],tomato).
But I always get exception error: no function clause matching
Maybe I misunderstood the basics, but here is the module code I'm trying to do:
-module(veggies).
-export([veggieMember/2]).
veggieMember(veggieList,query)->
case lists:member(query, veggieList) of
true->veggieList;
false->[query|veggieList]
end.
Binding in erlang starts with a capital letter. So it should be:
-module(veggies).
-export([veggieMember/2]).
veggieMember(VeggieList,Query)->
case lists:member(Query, VeggieList) of
true -> VeggieList;
false -> [Query|VeggieList]
end.
In your example it didn't work because there is no matching function clause. Atom veggieList doesn't match list [cucumber,tomato,potato] and atom query doesn't match atom tomato.
The error itself, it one of the standard errors. It means you have made a call to function and that none of the function clauses (separated by ;) matched.
I have user information coming in from an outside source and I need to check if that user is active. Sometimes I have a User and a Server and other times I have User#Server. The former case is no problem, I just have:
active(User, Server) ->
do whatever.
What I would like to do with the User#Server case is something like:
active([User, "#", Server]) ->
active(User, Server).
Doesn't seem to work. When calling active in the erlang terminal with a#b for example, I get an error that there is no match. Any help would be appreciated!
You can tokenize the string to get the result:
active(UserString) ->
[User,Server] = string:tokens(UserString,"#"),
active(User,Server).
If you need something more elaborate, or with better handling of something like email addresses, it might then be time to delve into using regular expressions with the re module.
active(UserString) ->
RegEx = "^([\\w\\.-]+)#([\\w\\.-]+)$",
{match, [User,Server]} = re:run(UserString,RegEx,[{capture,all_but_first,list}]),
active(User,Server).
Note: The supplied Regex is hardly sufficient for email address validation, it's just an example that allows all alphanumeric characters including underscores (\\w), dots (\\.), and dashes (-) seperated by an at symbol. And it will fail if the match doesn't stretch the whole length of the string: (^ to $).
A note on the pattern matching, for the real solution to your problem I think #chops suggestions should be used.
When matching patterns against strings I think it's useful to keep in mind that erlang strings are really lists of integers. So the string "#" is actually the same as [64] (64 being the ascii code for #)
This means that you match pattern [User, "#", Server] will match lists like: [97,[64],98], but not "a#b" (which in list form is [97,64,98]).
To match the string you need to do [User,$#,Server]. The $ operator gives you the ascii value of the character.
However this match pattern limits the matching string to be 1 character followed by # and then one more character...
It can be improved by doing [User, $# | Server] which allows the server part to have arbitrary length, but the User variable will still only match one single character (and I don't see a way around that).
I've been playing around with the splitting of atoms and have a problem with strings. The input data will always be an atom that consists of some letters and then some numbers, for instance ms444, r64 or min1. Since the function lists:splitwith/2 takes a list the atom is first converted into a list:
24> lists:splitwith(fun (C) -> is_atom(C) end, [m,s,4,4,4]).
{[m,s],[4,4,4]}
25> lists:splitwith(fun (C) -> is_atom(C) end, atom_to_list(ms444)).
{[],"ms444"}
26> atom_to_list(ms444).
"ms444"
I want to separate the letters from the numbers and I've succeeded in doing that when using a list, but since I start out with an atom I get a "string" as result to put into my splitwith function...
Is it interpreting each item in the list as a string or what is going on?
You might want to have a look at the string module documentation:
http://www.erlang.org/doc/man/string.html
The following function might interest you:
tokens(String, SeparatorList) -> Tokens
Since strings in Erlang are just a list() of integer() the test in the fun will be made if the item is an atom() when it is in fact an integer(). If the test is changed to look for letters it works:
29> lists:splitwith(fun (C) -> (C >= $a) and (C =< $Z) end, atom_to_list(ms444)).
{"ms","444"}
An atom in erlang is a named constant and not a variable (or not like a variable is in an imperative language).
You should really not create atoms in dynamic fashion (that is, don't convert things to atoms at runtime)
They are used more in pattern matching and send recive code.
Pid ! {matchthis, X}
recive
{foobar,Y} -> doY(Y);
{matchthis,X} -> doX(X);
Other -> doother(Other)
end
A variable, like X could be set to an atom. For example X=if 1==1 -> ok; true -> fail end. I could suffer from poor imagination but I can't think of a way why you would like to parse atom. You should be in charge of what atoms you write and not use list_to_atom(CharIntegerList).
Can you perhaps give a more overview of what you like to accomplish?
A "string" in Erlang is not a primitive type: it is just a list() of integers(). So if you want to "separate" the letters from the digits, you'll have to do comparison with the integer representation of the characters.